Semiconductor device and method of fabricating the same

ABSTRACT

A semiconductor device includes a substrate, a conductive pattern, a side spacer, and an air gap. The substrate includes an interlayer insulating layer and a trench penetrating the interlayer insulating layer. The conductive pattern is disposed within the trench of the substrate. The side spacer is disposed within the trench. The side spacer covers an upper side surface of the conductive pattern. The air gap is disposed within the trench. The air gap is bounded by a sidewall of the trench, the side spacer, and a lower side surface of the conductive pattern. A level of a bottom surface of the conductive pattern is lower than a level of bottom surfaces of the side spacer.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority under 35 U.S.C. §119 to Korean Patent Application No. 10-2013-0026388, filed on Mar. 12, 2013 in the Korean Intellectual Property Office, the disclosure of which is hereby incorporated by reference in its entirety.

TECHNICAL FIELD

The present inventive concept relates to a semiconductor device and a method of fabricating the same.

DISCUSSION OF RELATED ART

Conductive patterns serve to connect various elements incorporated in semiconductor devices. Capacitance between the conductive patterns may delay a signal propagation. As semiconductor devices are highly integrated, such signal delay decreases the performance thereof.

SUMMARY

According to an exemplary embodiment of the inventive concept, a semiconductor device includes a semiconductor substrate, a lower conductive pattern, an interlayer insulating layer, an upper conductive pattern, a side spacer, and an air gap. The lower conductive pattern is disposed on the semiconductor substrate. The interlayer insulating layer is disposed on the semiconductor substrate. The interlayer insulating layer includes an upper penetrating hole partially exposing a top surface of the lower conductive pattern. The upper conductive pattern is disposed within the upper penetrating hole and is disposed on the top surface of the lower conductive pattern. The upper conductive pattern is electrically connected to the lower conductive pattern. The side spacer is disposed within the upper penetrating hole. The side spacer covers an upper side surface of the upper conductive pattern. The air gap is disposed within the upper penetrating hole. The air gap is bounded by a sidewall of the upper penetrating hole, the side spacer, part of the top surface of the lower conductive pattern, and a lower side surface of the upper conductive pattern.

According to an exemplary embodiment of the inventive concept, a semiconductor device includes a substrate, a conductive pattern, a side spacer, and an air gap. The substrate includes an interlayer insulating layer and a trench penetrating the interlayer insulating layer. The conductive pattern is disposed within the trench of the substrate. The side spacer is disposed within the trench. The side spacer covers an upper side surface of the conductive pattern. The air gap is disposed within the trench. The air gap is bounded by a sidewall of the trench, the side spacer, and a lower side surface of the conductive pattern. A level of a bottom surface of the conductive pattern is lower than a level of bottom surfaces of the side spacer.

According to an exemplary embodiment of the inventive concept, a semiconductor device includes a semiconductor substrate, an interlayer insulating layer, a conductive pattern, an etch stop layer, a side spacer, and an air gap. The interlayer insulating layer is disposed on the semiconductor substrate. The interlayer insulating layer includes a trench penetrating the interlayer insulating layer. The conductive pattern is disposed within the trench. A bottom surface of the conductive pattern being contact with a bottom surface of the trench. The etch stop layer is disposed on the conductive pattern. The etch stop layer covers the trench. The side spacer covers a side surface of the conductive pattern. The side spacer is spaced from the interlayer insulating layer. The air gap is bounded by the interlayer insulating layer, the conductive pattern, the etch stop layer and the side spacer. A bottom surface of the side spacer is spaced from the bottom surface of the trench.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features of the inventive concept will become more apparent by describing in detail exemplary an exemplary embodiment thereof with reference to the accompanying drawings of which:

FIG. 1 is a cross-sectional view of a semiconductor device according to an exemplary embodiment of the inventive concept;

FIG. 2 is a cross-sectional view of a semiconductor device according to an exemplary embodiment of the inventive concept;

FIG. 3 is a cross-sectional view of a semiconductor device according to an exemplary embodiment of the inventive concept;

FIGS. 4A through 4R are cross-sectional views illustrating sequential operations of a method of fabricating a semiconductor device according to an exemplary embodiment of the inventive concept;

FIGS. 5A through 5G are cross-sectional views illustrating sequential operations of a method of fabricating a semiconductor device according to an exemplary embodiment of the inventive concept;

FIG. 6 is a diagram of a semiconductor module including a semiconductor device according to an exemplary embodiment of the inventive concept;

FIG. 7 is a diagram of a mobile system including a semiconductor device according to an exemplary embodiment of the inventive concept;

FIG. 8 is a diagram of a mobile device including a semiconductor device according to an exemplary embodiment of the inventive concept; and

FIG. 9 is a diagram of an electronic system including a semiconductor device according to an exemplary embodiment of the inventive concept.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Exemplary an exemplary embodiment of the inventive concept will be described below in detail with reference to the accompanying drawings. However, the inventive concept may be embodied in different forms and should not be construed as limited to the exemplary embodiment set forth herein. In the drawings, the thickness of layers and regions may be exaggerated for clarity. It will also be understood that when a layer is referred to as being “on” another layer or substrate, it may be directly on the other layer or substrate, or intervening layers may also be present. Like reference numerals may refer to the like elements throughout the specification and drawings.

FIG. 1 is a cross-sectional view of a semiconductor device 100 a according to an exemplary embodiment of the inventive concept.

Referring to FIG. 1, a semiconductor device 100 a includes a semiconductor substrate 100, a lower interlayer insulating layer 110, a lower conductive pattern 120 p, a lower etch stop layer 130, an upper interlayer insulating layer 140, side spacers 160 s, an upper conductive pattern 170 p, an upper etch stop layer 180, and an air gap 190 a.

The semiconductor substrate 100 may include a silicon wafer or a silicon-on-insulator (SOI) substrate. The lower interlayer insulating layer 110 is disposed on the semiconductor substrate 100. Various elements may be disposed between the semiconductor substrate 100 and the lower interlayer insulating layer 110. The lower interlayer insulating layer 110 may cover the various elements disposed on the semiconductor substrate 100. The lower interlayer insulating layer 110 may include tetraethyl orthosilicate (TEOS).

The lower conductive pattern 120 p is disposed in the lower interlayer insulating layer 110. The lower conductive pattern 120 p may be electrically connected to at least one of various elements disposed between the semiconductor substrate 100 and the lower interlayer insulating layer 110. The lower conductive pattern 120 p penetrates the lower interlayer insulating layer 110. A level of a top surface of the lower conductive pattern 120 p is substantially the same as a level of a top surface of the lower interlayer insulating layer 110. The lower interlayer insulating layer 110 surrounds a side surface of the lower conductive pattern 120 p.

The lower conductive pattern 120 p may include a conductive material. For example, the lower conductive pattern 120 p may include tungsten (W).

The lower conductive pattern 120 p includes a first recess region 121 r and a second recess region 122 r.

The first recess region 121 r is disposed in the top surface of the lower conductive pattern 120 p. A maximum horizontal width of the first recess region 121 r is less than a horizontal width of the top surface of the lower conductive pattern 120 p. A level of a bottom surface of the first recess region 121 r is lower than a level of the top surface of the lower conductive pattern 120 p. A level of the bottom surface of the first recess region 121 r is lower than a level of the top surface of the lower interlayer insulating layer 110.

The second recess region 122 r is disposed in the top surface of the lower conductive pattern 120 p. The second recess region 122 r is disposed in the first recess region 121 r. A maximum horizontal width of the second recess region 122 r is less than the maximum horizontal width of the first recess region 121 r. A horizontal width of the second recess region 122 r in the bottom surface of the first recess region 121 r is less than a horizontal width of the bottom surface of the first recess region 121 r. A level of a bottom surface of the second recess region 122 r is lower than a level of the bottom surface of the first recess region 121 r. A sidewall of the second recess region 122 r need not be parallel to a sidewall of the first recess region 121 r.

The lower etch stop layer 130 is disposed on the lower interlayer insulating layer 110. The lower etch stop layer 130 is in contact with the top surface of the lower interlayer insulating layer 110.

The lower etch stop layer 130 may have a different etch rate from the lower interlayer insulating layer 110. The lower etch stop layer 130 may have etch selectivity with respect to the lower interlayer insulating layer 110. The lower etch stop layer 130 may be harder than the lower interlayer insulating layer 110. For instance, the lower etch stop layer 130 may include silicon nitride (SiN) or silicon carbon nitride (SiCN).

The lower etch stop layer 130 includes a lower penetrating hole 130 h. The lower penetrating hole 130 h penetrates the lower etch stop layer 130. The lower penetrating hole 130 h partially exposes the top surface of the lower conductive pattern 120 p. The lower penetrating hole 130 h exposes the first recess region 121 r of the lower conductive pattern 120 p.

A sidewall of the lower penetrating hole 130 h corresponds to an extension line of the sidewall of the first recess region 121 r. A horizontal width of the lower penetrating hole 130 h measured at a bottom surface of the lower etch stop layer 130 is substantially equal to a horizontal width of the first recess region 121 r measured at the top surface of the lower conductive pattern 120 p. A horizontal width of the lower penetrating hole 130 h measured at the top surface of the lower interlayer insulating layer 110 is substantially equal to a horizontal width of the first recess region 121 r measured at the top surface of the lower interlayer insulating layer 110.

The upper interlayer insulating layer 140 is disposed on the lower etch stop layer 130. The lower etch stop layer 130 is interposed between the lower interlayer insulating layer 110 and the upper interlayer insulating layer 140. The lower etch stop layer 130 is interposed between the lower conductive pattern 120 p and the upper interlayer insulating layer 140. The upper interlayer insulating layer 140 is in contact with the top surface of the lower etch stop layer 130.

The upper interlayer insulating layer 140 may have a different etch rate from the lower etch stop layer 130. The upper interlayer insulating layer 140 may have etch selectivity with respect to the lower etch stop layer 130. The upper interlayer insulating layer 140 may include a material having a low dielectric constant. For instance, the upper interlayer insulating layer 140 may include a low-k dielectric layer.

The upper interlayer insulating layer 140 includes an upper penetrating hole 140 h. The upper penetrating hole 140 h penetrates the upper interlayer insulating layer 140. The upper penetrating hole 140 h exposes the lower penetrating hole 130 h. The upper penetrating hole 140 h exposes the first recess region 121 r of the lower conductive pattern 120 p.

A trench 140 t includes the first recess region 121 r, the lower penetrating hole 130 h, and the upper penetrating hole 140 h. A sidewall of the trench 140 t includes the sidewall of the lower penetrating hole 130 h, a sidewall of the upper penetrating hole 140 h, and the sidewall of the first recess region 121 r. A level of a bottom surface of the trench 140 t is substantially the same as a level of a bottom surface of the first recess region 121 r. The trench 140 t partially exposes the top surface of the lower conductive pattern 120 p. The trench 140 t penetrates the upper interlayer insulating layer 140.

The side spacers 160 s are disposed within the trench 140 t. A level of top surfaces of the side spacers 160 s is substantially the same as a level of a top surface of the upper interlayer insulating layer 140. The side spacers 160 s are disposed on the top surface of the lower conductive pattern 120 p. The side spacers 160 s are disposed on the bottom surface of the first recess region 121 r. The side spacers 160 s need not vertically overlap the bottom surface of the second recess region 122 r.

The side spacers 160 s are spaced apart from the sidewall of the trench 140 t. The side spacers 160 s are spaced apart from the sidewall of the lower penetrating hole 130 h, the sidewall of the upper penetrating hole 140 h, and the sidewall of the first recess region 121 r. The side spacers 160 s are spaced apart from the bottom surface of the trench 140 t. The side spacers 160 s are spaced apart from the bottom surface of the first recess region 121 r. A level of bottom surfaces of the side spacers 160 s is higher than a level of the bottom surface of the first recess region 121 r. A level of the bottom surfaces of the side spacers 160 s is higher than a level of the top surface of the lower conductive pattern 120 p.

The side spacers 160 s are disposed on a sidewall of the upper conductive pattern 170 p. The side spacers 160 s are in contact with the side surface of the upper conductive pattern 170 p. Each of the side spacers 160 s includes a first side surface S1 and a second side surface S2.

The first side surface S1 of each of the side spacers 160 s is in contact with the side surface of the upper conductive pattern 170 p. The first side surface S1 of each of the side spacers 160 s corresponds to an extension line of the sidewall of the second recess region 122 r.

The second side surface S2 of the side spacers 160 s is opposite to the first side surface S1 of the side spacers 160 s. The second side surface S2 of the side spacers 160 s faces the sidewall of the trench 140. The second side surface S2 of each of the side spacers 160 s faces the sidewall of the lower penetrating hole 130 h and the sidewall of the upper penetrating hole 140 h.

The second side surface S2 of each of the side spacers 160 s may be parallel to the facing sidewall of the trench 140 t. The second side surface S2 of each spacer 160 s partially overlaps the lower penetrating hole 130 h and is parallel to the sidewall of the lower penetrating hole 130 h. The second side surface S2 partially overlaps the upper penetrating hole 140 h and is parallel to the sidewall of the upper penetrating hole 140 h. A horizontal distance between the second side surface S2 and the sidewall of the lower penetrating hole 130 h is substantially equal to a horizontal distance between the second side surface S2 and the sidewall of the upper penetrating hole 140 h.

The bottom surfaces of the side spacers 160 s are parallel to the bottom surface of the first recess region 121 r. A vertical distance between the bottom surface of each of the side spacers 160 s and the bottom surface of the first recess region 121 r may be equal to the horizontal distance between the second side surface S2 of each of the side spacers 160 s and the sidewall of the first recess region 121 r. The vertical distance between the bottom surface of each side spacer 160 s and the bottom surface of the first recess region 121 r may be substantially equal to the horizontal distance between the second side surface S2 of each of the side spacers 160 s and the sidewall of the lower penetrating hole 130 h. The vertical distance between the bottom surface of each of the side spacers 160 s and the bottom surface of the first recess region 121 r may be equal to the horizontal distance between the second side surface S2 of each of the side spacers 160 s and the sidewall of the upper penetrating hole 140 h.

The side spacers 160 s may have a different etch rate from the upper interlayer insulating layer 140. The side spacers 160 s may have an etch selectivity with respect to the upper interlayer insulating layer 140. The side spacers 160 s may include the substantially same material as the lower etch stop layer 130. For example, the side spacers 160 s may include SiCN.

The upper conductive pattern 170 p is electrically connected to the lower conductive pattern 120 p. The upper conductive pattern 170 p is disposed within the trench 140 t. A level of a top surface of the upper conductive pattern 170 p is substantially the same as a level of the top surface of the upper interlayer insulating layer 140. A level of the top surface of the upper conductive pattern 170 p is substantially the same as a level of the top surfaces of the side spacers 160 s. The upper conductive pattern 170 p is interposed between the side spacers 160 s.

A level of a bottom surface of the upper conductive pattern 170 p is lower than a level of the bottom surfaces of the side spacers 160 s. The upper conductive pattern 170 p is extended into the first recess region 121 r of the lower conductive pattern 120 p. The upper conductive pattern 170 p is further extended into the second recess region 122 r of the lower conductive pattern 120 p. A level of the bottom surface of the upper conductive pattern 170 p is lower than a level of the bottom surface of the trench 140 t. A level of the bottom surface of the upper conductive pattern 170 p is lower than a level of the bottom surface of the first recess region 121 r. The upper conductive pattern 170 p is in contact with the lower conductive pattern 120 p. A level of the bottom surface of the upper conductive pattern 170 p is substantially the same as a level of the bottom surface of the second recess region 122 r.

The upper conductive pattern 170 p completely fills the second recess region 122 r. A horizontal width of the bottom surface of the upper conductive pattern 170 p is substantially equal to a horizontal width of the bottom surface of the second recess region 122 r.

The upper conductive pattern 170 p includes a barrier pattern 171 p and a metal pattern 173 p.

The barrier pattern 171 p covers side and bottom surfaces of the metal pattern 173 p. The barrier pattern 171 p is in contact with the side spacers 160 s. The barrier pattern 171 p is in contact with the second recess region 122 r. The barrier pattern 171 p is in contact with the sidewall and bottom surface of the second recess region 122 r. The barrier pattern 171 p may include tantalum (Ta) or tantalum nitride (TaN). The barrier pattern 171 p may include a stack structure of a Ta pattern and a TaN pattern.

The metal pattern 173 p is disposed in the barrier pattern 171 p. The side and bottom surfaces of the metal pattern 173 p are surrounded by the barrier pattern 171. The metal pattern 173 p may include a metal material. For example, the metal pattern 173 may include copper (Cu).

The upper etch stop layer 180 is disposed on the upper interlayer insulating layer. The upper etch stop layer 180 is disposed on the side spacers 160 s. The upper etch stop layer 180 is disposed on the upper conductive pattern 170 p. The upper etch stop layer 180 is in contact with the upper interlayer insulating layer 140, the side spacers 160 s, and the upper conductive pattern 170 p. A level of a bottom surface of the upper etch stop layer 180 is substantially the same as a level of the top surface of the upper interlayer insulating layer 140. A level of the upper etch stop layer 180 is substantially the same as a level of the top surfaces of the side spacers 160 s. A level of the upper etch stop layer 180 is substantially the same as a level of the top surface of the upper conductive pattern 170 p.

The upper etch stop layer 180 may have a different etch rate from the upper interlayer insulating layer 140. The upper etch stop layer 180 may have etch selectivity with respect to the upper interlayer insulating layer 140. The upper etch stop layer 180 may include substantially the same material as the side spacers 160 s. For example, the upper etch stop layer 180 may include SIGN. The upper etch stop layer 180 may be harder than the side spacers 160 s.

The air gap 190 a is disposed within the trench 140 t. The air gap 190 a is interposed between the trench 140 t and the side spacers 160 s. The air gap 190 a is interposed between the sidewall of the trench 140 t and the second side surface S2 of each side spacer 160 s, and between the bottom surface of the trench 140 t and the bottom surface of each side spacer 160 s. The air gap 190 a is extended along the sidewall and bottom surface of the trench 140 t. The air gap 190 a is interposed between the sidewall of the upper penetrating hole 140 h and the second side surface S2 of each side spacer 160 s. The air gap 190 a is interposed between the sidewall of the lower penetrating hole 130 h and the second side surface S2. The air gap 190 a is interposed between the bottom surface of the first recess region 121 r and the bottom surface of each side spacer 160 s. The air gap 190 a is extended along the sidewall of the upper penetrating hole 140 h, the sidewall of the lower penetrating hole 130 h, and the top surface of the lower conductive pattern 120 p.

The air gap 190 a is defined by the lower conductive pattern 120 p, the lower etch stop layer 130, the upper interlayer insulating layer 140, the side spacer 160 s, the upper conductive pattern 170 p, and the upper etch stop layer 180. A lowest level of the air gap 190 a is substantially the same as a level of the bottom surface of the first recess region 121 r of the lower conductive pattern 120 p. The lowest level of the air gap 190 a is substantially the same as a level of the bottom surface of the trench 140 t. A highest level of the air gap 190 a is substantially the same as a level of the bottom surface of the upper etch stop layer 180. The highest level of the air gap 190 a is substantially the same as a level of the top surface of the upper interlayer insulating layer 140. The highest level of the air gap 190 a is substantially the same as a level of the top surface of each of the side spacers 160 s The highest level of each of the air gaps 190 a is substantially the same as a level of the top surface of the upper conductive pattern 170 p.

The air gap 190 a is extended along the top surface of the lower conductive pattern 120 p to the side surface of the upper conductive pattern 170 p. The air gap 190 a exposes part of the side surface of the upper conductive pattern 170 p. The exposed part of the upper conductive pattern 170 p is disposed between the top surface of the lower conductive pattern 120 p and the bottom surface of each of the side spacers 160 s. The side surface of the upper conductive pattern 170 p may be partially exposed by the air gap 190 a.

The side surface of the upper conductive pattern 170 p partially exposed by the air gap 190 a corresponds to the extension line of the side surface of the second recess region 122 r. The side surface of the upper conductive pattern 170 p partially exposed by the air gap 190 a corresponds to an extended boundary line between the upper conductive pattern 170 p and each side spacer 160 s. The side surface of the upper conductive pattern 170 p partially exposed by the air gap 190 a may correspond to an extension line of the first side surface S1 of each side spacer 160 s. The sidewall of the second recess region 122 r corresponds to the extension line of the first side surface S1 of each of the side spacers 160 s.

In the semiconductor device according to an exemplary embodiment of the inventive concept, the air gap 190 a is interposed between the side spacers 160 s of the upper conductive pattern 170 p and the trench 140 t. For example, the side surface of the upper conductive pattern 170 p is surrounded by the air gap 190 a. Thus, capacitance between the upper conductive pattern 170 p and other adjacent conductive patterns may be reduced, thereby decreasing a signal delay time of the upper conductive pattern 170 p.

FIG. 2 is a cross-sectional view of a semiconductor device according to an exemplary embodiment of the inventive concept.

Referring to FIG. 2, a semiconductor device according to the embodiments of the inventive concept includes a semiconductor substrate 100, a lower interlayer insulating layer 110, a lower conductive pattern 120 p, a lower etch stop layer 130, an upper interlayer insulating layer 140, side spacers 160 s, an Upper conductive pattern 170 p, an upper etch stop layer 180, and an air gap 190 a.

The lower conductive pattern 120 p includes a first recess region 121 r. The first recess region 121 r is disposed in a top surface of the lower conductive pattern 120 p. An upper penetrating hole 140 h of the upper interlayer insulating layer 140 partially exposes a bottom surface of the first recess region 121 r.

A horizontal width w of each side spacer 160 s is less than a distance between a trench 140 t and the side spacer 160 s. The horizontal width w of each side spacer 160 s is less than a horizontal distance between the side spacer 160 s and a sidewall of the upper penetrating hole 140 h. The horizontal width w of each side spacer 160 s is less than a horizontal distance between the side spacer 160 s and a sidewall of the lower penetrating hole 130 h of the lower etch stop layer 130. The horizontal width w of each of the side spacers 160 s is less than a vertical distance between a bottom surface of each side spacer 160 s and the bottom surface of the first recess region 121 r.

A level of a bottom surface of the upper conductive pattern 170 p is substantially the same as a level of the bottom surface of the first recess region 121 r. A level of the bottom surface of the upper conductive pattern 170 p is substantially the same as a level of a bottom surface of the trench 140 t. A level of the bottom surface of the upper conductive pattern 170 p is substantially the same as a level of a lowest level of the air gap 190 a.

FIG. 3 is a cross-sectional view of a semiconductor device according to an exemplary embodiment of the inventive concept.

Referring to FIG. 3, a semiconductor device according to an exemplary embodiment of the inventive concept includes a semiconductor substrate 100, a lower interlayer insulating layer 110, a lower conductive pattern 120 p, a lower etch stop layer 130, an upper interlayer insulating layer 140, side spacers 160 s, an upper conductive pattern 170 p, an upper etch stop layer 180, and an air gap 190 a.

The lower conductive pattern 120 p includes a first recess region 121 r. A bottom surface of the upper conductive pattern 170 p is substantially at the same level as a bottom surface of the first recess region 121 r. A horizontal width w of each side spacer 160 s is less than a distance between a trench 140 t and the side spacer 160 s.

A horizontal width of a top surface of each side spacer 160 s is less than a horizontal width of a bottom surface thereof. A first side surface S1 of each side spacer 160 s includes a curved region 160 c that is bent toward a second side surface S2 of each side spacer 160 s. The curved region 160 c is disposed close to the upper etch stop layer 180.

FIGS. 4A through 4R are cross-sectional views illustrating a method of fabricating a semiconductor device according to an exemplary embodiment of the inventive concept.

A method of fabricating the semiconductor device according to an exemplary embodiment of the inventive concept will now be described with reference to FIGS. 1 and 4A through 4R. Referring to FIG. 4A, the method of fabricating the semiconductor device according to an exemplary embodiment of the inventive concept includes forming a lower interlayer insulating layer 110, a lower conductive pattern 120 p, and a lower etch stop layer 130 on a semiconductor substrate 100.

The formation of the lower interlayer insulating layer 110, the lower conductive pattern 120 p, and the lower etch stop layer 130 on the semiconductor substrate 100 includes preparing the semiconductor substrate 100, forming the lower interlayer insulating layer 110 on the semiconductor substrate 100, forming the lower conductive pattern 120 p on the semiconductor substrate 100, and forming the lower etch stop layer 130 on the lower interlayer insulating layer 110 and the lower conductive pattern 120 p.

Referring to FIG. 4B, an upper interlayer insulating layer 140 is formed on the lower etch stop layer 130.

The upper interlayer insulating layer 140 may include a material having a different etch rate from the lower etch stop layer 130. For example, the upper interlayer insulating layer 140 may include a dielectric layer having a low dielectric constant.

Referring to FIG. 4C, a first mask pattern 410 is formed on the upper interlayer insulating layer 140.

A preliminary first mask pattern layer is formed on the upper interlayer insulating layer 140, and then the preliminary first mask pattern layer is patterned to form the first mask pattern 410 having a first mask hole 410 h. The first mask hole 410 h exposes part of the upper interlayer insulating layer 140. The first mask hole 410 h is disposed on a top surface of the lower conductive pattern 120 p. The first mask pattern 410 may include a photoresist pattern.

Referring to FIG. 4D, an upper penetrating hole 140 h is formed in the upper interlayer insulating layer 140 using the first mask pattern 410.

The upper penetrating hole 140 h partially exposes a top surface of the lower etch stop layer 130. The formation of the upper penetrating hole 140 h includes etching the upper interlayer insulating layer 140 using the first mask pattern 410.

Referring to FIG. 4E, a trench 140 t is formed on the semiconductor substrate 100.

The formation of the trench 140 t includes forming a lower penetrating hole 130 h in the lower etch stop layer 130, and forming a first recess region 121 r in the top surface of the lower conductive pattern 120 p. The trench 140 t includes the first recess region 121 r, the lower penetrating hole 130 h, and the upper penetrating hole 140 h. The trench 140 t includes the first recess region 121 r, the lower penetrating hole 130 h, and the upper penetrating hole 140 h.

The formation of the lower penetrating hole 130 h in the lower etch stop layer 130 includes etching the lower etch stop layer 130 using the first mask pattern 410.

The formation of the first recess region 121 r in the top surface of the lower conductive pattern 120 p includes recessing the top surface of the lower conductive pattern 120 p exposed by the lower penetrating hole 130 h. The recessing of the top surface of the lower conductive pattern 120 p exposed by the lower penetrating hole 130 h may be performed simultaneously with a process of etching the lower etch stop layer 130 using the first mask pattern 410.

Referring to FIG. 4F, the first mask pattern 410 is removed.

Referring to FIG. 4G, a sacrificial liner insulating layer 150 is formed on the upper interlayer insulating layer 140.

The formation of the sacrificial liner insulating layer 150 includes covering a sidewall and bottom surface of the trench 140 t with the sacrificial liner insulating layer 150. The formation of the sacrificial liner insulating layer 150 includes forming an insulating layer on the sidewall and bottom surface of the trench 140 t to a predetermined thickness. The formation of the sacrificial liner insulating layer 150 may be performed using an atomic layer deposition (ALD) process or a plasma-enhanced ALD (PEALD) process.

The sacrificial liner insulating layer 150 may include a material having a different etch rate from the upper interlayer insulating layer 140. The sacrificial liner insulating layer 150 may have etch selectivity with respect to the upper interlayer insulating layer 140. For example, the formation of the sacrificial liner insulating layer 150 may include forming a silicon oxide (SiO) layer using a first silicon precursor. The first silicon precursor may contain a silane-based material.

Referring to FIG. 4H, a spacer insulating layer 160 is formed on the sacrificial liner insulating layer 150.

The insulating layer is formed on a top surface of the sacrificial liner insulating layer 150 in a predetermined thickness. The formation of the spacer insulating layer 160 may be performed using an ALD process or a PEALD process.

The spacer insulating layer 160 may include a material having a different etch rate from the sacrificial liner insulating layer 150. The spacer insulating layer 160 may have etch selectivity with respect to the sacrificial liner insulating layer 150. For example, the formation of the spacer insulating layer 160 may include forming a SiCN layer on the sacrificial liner insulating layer 150 using a second silicon precursor. The second silicon precursor may be a silane-based material. The second silicon precursor may be substantially the same material as the first silicon precursor.

The process of forming the spacer insulating layer 160 may be performed in-situ together with the process of forming the sacrificial liner insulating layer 150. For example, the semiconductor substrate 100 having the trench 140 t may be loaded into a process chamber. The first silicon precursor may be supplied into the process chamber, and the sacrificial liner insulating layer 150 may be formed by reacting the first silicon precursor with oxygen plasma in the process chamber. The first silicon precursor may be purged from the process chamber, and then the top surface of the sacrificial liner insulating layer 150 with nitrogen plasma. The second silicon precursor may be supplied into the process chamber, and the spacer insulating layer 160 may be formed by reacting the second silicon precursor with nitrogen plasma. The second silicon precursor may be purged from the process chamber.

The spacer insulating layer 160 and the sacrificial liner insulating layer 150 may be formed using an in-situ process. Thus, thickness variation of the sacrificial liner insulating layer 150 may be reduced due to exposure to the atmosphere.

The nitrogen plasma may be generated using higher power than the oxygen plasma. For example, the oxygen plasma is generated using about 100 W power, and nitrogen plasma is generated using about 200 W power.

Referring to FIG. 4I, a planarization layer 210 is formed on the spacer insulating layer 160.

The formation of the planarization layer 210 includes filling the trench 140 t with the planarization layer 210. The planarization layer 210 may include a material having high fluidity. For example, the planarization layer 210 may include forming the planarization layer 210 using SOH.

Referring to FIG. 4J, a second mask pattern 420 is formed on the planarization layer 210.

The formation of the second mask pattern 420 may include forming a preliminary second mask pattern layer, and then patterning the preliminary second mask pattern layer to form the second mask pattern 420 having a second mask hole 420 h. The second mask hole 420 h exposes part of the planarization layer 210, and is disposed on a top surface of the lower conductive pattern 120. A horizontal width of the second mask hole 420 h is less than a horizontal width of the bottom surface of the trench 140 t. For example, the horizontal width of the second mask hole 420 h may be substantially equal to a maximum horizontal distance between sidewalk of the spacer insulating layer 160 disposed on sidewalls of the trench 140 t. The second mask pattern 420 may be substantially similar to the first mask pattern 410. For example, the second mask pattern 420 may include a photoresist pattern.

Referring to FIG. 4K, a second recess region 122 r is formed in the top surface of the lower conductive pattern 120 p formed on the semiconductor substrate 100.

The formation of the second recess region 122 r may include forming a planarization penetrating hole 210 h in the planarization layer 210, forming a spacer penetrating hole 160 h in the spacer insulating layer 160, forming a liner penetrating hole 150 h in the sacrificial liner insulating layer 150, and recessing the top surface of the lower conductive pattern 120 p.

The formation of the planarization penetrating hole 210 h in the planarization layer 210 may include etching the planarization layer 210 using the second mask pattern 420.

The formation of the spacer penetrating hole 160 h in the spacer insulating layer 160 may include etching the spacer insulating layer 160 using the second mask pattern 420. The etching of the spacer insulating layer 160 using the second mask pattern 420 may be performed simultaneously with the etching of the planarization layer 210 using the second mask pattern 420.

The formation of the liner penetrating hole 150 h in the sacrificial liner insulating layer 150 may include etching the sacrificial liner insulating layer 150 using the second mask pattern 420. The etching of the sacrificial liner insulating layer 150 using the second mask pattern 420 may be performed simultaneously with the etching of the spacer insulating layer 160 using the second mask pattern 420.

The recessing of the top surface of the lower conductive pattern 120 p may include recessing the top surface of the lower conductive pattern 120 p exposed by the liner penetrating hole 150 h. The recessing of the top surface of the lower conductive pattern 120 p exposed by the liner penetrating hole 150 h may be performed simultaneously with the etching of the sacrificial liner insulating layer 150 using the second mask pattern 420.

Referring to FIG. 4L, the second mask pattern 420 and the planarization layer 210 are removed.

Referring to FIG. 4M, the method of fabricating the semiconductor device according to an exemplary embodiment of the inventive concept may include forming a barrier layer 171 on the spacer insulating layer 160.

The formation of the barrier layer 171 includes covering a sidewall of the spacer penetrating hole 160 h, a sidewall of the liner penetrating hole 150 h, and a sidewall and bottom surface of the second recess region 122 r with the barrier layer 171.

Referring to FIG. 4N, a seed layer 172 is formed on the barrier layer 171.

The formation of the seed layer 172 may include forming the seed layer 172 using substantially the same material as a metal layer 173 to be formed using a subsequent process.

Referring to FIG. 4O, an upper conductive layer 170 is formed on the seed layer 172, filling a region surrounded by the trench 140 t.

The formation of the upper conductive layer 170 includes forming the metal layer 173 on the seed layer 172.

The formation of the metal layer 173 includes filling the spacer penetrating hole 160 h, the liner penetrating hole 150 h, and the second recess region 122 r with the metal layer 173. The formation of the metal layer 173 includes filling a space between sidewalls of the spacer insulating layer 160 disposed on the sidewalls of the trench 140 t with the metal layer 173. The formation of the metal layer 173 may be performed using an electroplating process.

Referring to FIG. 4P, a preliminary metal pattern 173 e is formed on the semiconductor substrate 100.

The formation of the preliminary metal pattern 173 e includes planarizing the metal layer 173 to expose a top surface of the barrier layer 171. The planarization of the metal layer 173 may be performed using a chemical mechanical polishing (CMP) process.

Referring to FIG. 4Q, a sacrificial liner pattern 150 s, a side spacer 160 s, and an upper conductive pattern 170 p are formed on the semiconductor substrate 100.

The formation of the sacrificial liner pattern 150 s, the side spacer 160 s, and the upper conductive pattern 170 p includes planarizing the sacrificial liner insulating layer 150, the spacer insulating layer 160, the barrier layer 171, and the preliminary metal pattern 173 e to expose a top surface of the upper interlayer insulating layer 140. The planarization of the sacrificial liner insulating layer 150, the spacer insulating layer 160, the barrier layer 171, and the preliminary metal pattern 173 e may be performed using a CMP process. The upper conductive pattern 170 p includes a barrier metal 171 p and a metal pattern 173 p.

The formation of the sacrificial liner pattern 150 s, the side spacer 160 s, and the upper conductive pattern 170 p may be performed in the same chamber as the process of forming the preliminary metal pattern 173 e.

Referring to FIG. 4R, an air gap 190 a is formed in the trench 140 t.

The formation of the air gap 190 a in the trench 140 t includes removing the sacrificial liner pattern 150 s.

The sacrificial liner pattern 150 s may include a material having a different etch rate from the upper interlayer insulating layer 140 and the side spacer 160 s. Thus, the sacrificial liner pattern 150 s is selectively removed to form the air gap 190 a.

Forming of the sacrificial liner insulating layer 150 and the spacer insulating layer 160 using an in-situ process, and forming the sacrificial liner pattern 150 s and the side spacer 160 s may reduce the number of processes required to form the sacrificial liner pattern 150 s and the side spacer 160 s, thereby increasing process efficiency.

Referring to FIG. 1, an upper etch stop layer 180 on the trench 140 t is formed to cover the air gap 190 a.

FIGS. 5A through 5G are cross-sectional views illustrating sequential operations of a method of fabricating a semiconductor device according to an exemplary embodiment of the inventive concept.

The method of fabricating the semiconductor device according to an exemplary embodiment of the inventive concept will now be described with reference to FIGS. 2 and 5A through 5G. To begin with, referring to FIG. 5A, the method of fabricating the semiconductor device according to an exemplary embodiment of the inventive concept includes preparing a semiconductor substrate 100, forming a lower interlayer insulating layer 110 on the semiconductor substrate 100, forming a lower conductive pattern 120 p on the semiconductor substrate 100, forming a lower etch stop layer 130 on the lower interlayer insulating layer 110 and the lower conductive pattern 120 p, forming an upper interlayer insulating layer 140 on the lower etch stop layer 130, forming a trench 140 t through the upper interlayer insulating layer 140, forming a sacrificial liner insulating layer 150 to cover a sidewall and bottom surface of the trench 1401, and forming a spacer insulating layer 160 on the sacrificial liner insulating layer 150.

Referring to FIG. 5B, a first preliminary side spacer 161 s is formed on the sacrificial liner insulating layer 150.

The formation of the first preliminary side spacer 161 s includes etching the spacer insulating layer 160. For example, the formation of the first preliminary side spacer 161 s may include anisotropically etching the spacer insulating layer 160.

The first preliminary side spacer 161 s includes a first preliminary curved region 161 c. The first preliminary curved region 161 c may be disposed close to a top surface of the first preliminary side spacer 161 s.

Referring to FIG. 5C, a sacrificial spacer 151 s and a second preliminary side spacer 162 s are formed within the trench 140 t.

The formation of the sacrificial spacer 151 s and the second preliminary side spacer 162 s may include etching the sacrificial liner insulating layer 150 and the first preliminary side spacer 161 s. For example, the formation of the sacrificial spacer 151 s and the second preliminary side spacer 162 s may include anisotropically etching the sacrificial liner insulating layer 150 and the first preliminary side spacer 161 s.

The anisotropic etching of the sacrificial liner insulating layer 150 and the first preliminary side spacer 161 s may be performed simultaneously with the process of anisotropically etching the spacer insulating layer 160. FIG. 5B may be a cross-sectional view of a shape formed in the middle of the corresponding process.

The sacrificial spacer 151 s includes a sacrificial curved region 151 c. The sacrificial curved region 151 c is disposed close to a top surface of the sacrificial spacer 151 s.

The second preliminary side spacer 162 s includes a second preliminary curved region 162 c. The second preliminary curved region 162 c is disposed close to a top surface of the second preliminary side spacer 162 s. A surface of the second preliminary curved region 162 c may correspond to an extension line of a surface of the sacrificial curved region 151 c. Alternatively, the surface of the second preliminary curved region 162 c may have substantially the same curvature as the surface of the sacrificial curved region 151 c.

Referring to FIG. 5D, a barrier layer 171 is formed on the upper interlayer insulating layer 140.

The formation of the barrier layer 171 includes forming the barrier layer 171 to cover the sacrificial spacer 151 s and the second preliminary side spacer 162 s.

Referring to FIG. 5E, the method of fabricating the semiconductor device according to an exemplary embodiment of the inventive concept may include forming an upper conductive layer 170 to fill the trench 140 t.

The formation of the upper conductive layer 170 includes forming a metal layer 173 on the barrier layer 171.

Referring to FIG. 5F, a preliminary metal pattern 173 e is formed to fill the trench 140 t.

The formation of the preliminary metal pattern 173 e includes planarizing the metal layer 173 to expose a top surface of the barrier layer 171.

Referring to FIG. 50, a sacrificial liner pattern 150 s, a side spacer 160 s, a barrier pattern 171 p, and a metal pattern 173 p are formed to fill the trench 140 t.

The formation of the sacrificial liner pattern 150 s, the side spacer 160 s, the barrier pattern 171 p, and the metal pattern 173 p includes planarizing the upper interlayer insulating layer 140, the sacrificial spacer 151 s, the second preliminary side spacer 162 s, the barrier layer 171, and the preliminary metal pattern 173 e to remove the sacrificial curved region 151 c and the second preliminary curved region 162 c. The planarization of the upper interlayer insulating layer 140, the sacrificial spacer 151 s, the second preliminary side spacer 162 s, the barrier layer 171, and the preliminary metal pattern 173 e is performed using a CMP process.

An upper conductive pattern 170 p includes the barrier pattern 171 p and the metal pattern 173 p.

Referring to FIG. 2, an air gap 190 a is formed in the trench 140 t by removing the sacrificial liner pattern 150 s, and an upper etch stop layer 180 is formed on the trench 140 t.

The formation of the air gap 190 a in the trench 140 t includes removing the sacrificial liner pattern 150 s.

FIG. 6 is a diagram of a semiconductor module 1000 including a semiconductor device according to an exemplary embodiment of the inventive concept.

Referring to FIG. 6, the semiconductor module 1000 includes a module substrate 1100, memories 1200, a microprocessor (MP) 1300, and input/output (i/O) terminals 1400. The memories 1200, the MP 1300, and the I/O terminals 1400 are mounted on the module substrate 1100. The semiconductor module 1000 may include a memory card or a card package.

Each of the memories 1200 and the MP 1300 may include a semiconductor device according to an exemplary embodiment of the inventive concept. Accordingly, operation speeds of the memories 1200 and the MP 1300 may be increased.

FIG. 7 is a diagram of a mobile system 2000 including a semiconductor device according to an exemplary embodiment of the inventive concept.

Referring to FIG. 7, the mobile system 2000 includes a display unit 2100, a body unit 2200, and an external apparatus 2300. The body unit 2200 includes an MP 2210, a power supply 2220, a function unit 2230, and a display controller 2240.

The display unit 2100 is electrically connected to the body unit 2200. The display unit 2100 is electrically connected to the display controller 2240 of the body unit 2200. The display unit 2100 displays an image processed by the display controller 2240 of the body unit 2200.

The body unit 2200 includes a system board or motherboard including a printed circuit board (PCB). The MP 2210, the power supply 2220, the function unit 2230, and the display controller 2240 are mounted on the body unit 2200.

The MP 2210 receives a voltage from the power supply 2230 and controls the function unit 2230 and the display controller 2240. The power supply 2220 receives a predetermined voltage from an external power supply, divide the predetermined voltage into various voltage levels, and supply the divided voltages to the MP 2210, the function unit 2230, and the display controller 2240.

The power supply 2220 includes a power management IC (PMIC). The PMIC efficiently supplies voltages to the MP 2210, the function unit 2230, and the display controller 2240.

The function unit 2230 serves various functions of the mobile system 2000. For example, the function unit 2230 may include several elements capable of wireless communication functions, such as output of an image to the display unit 2100 or output of a voice to a speaker, by dialing or communication with the external apparatus 2300. For example, the functional unit 2230 may serve as an image processor of a camera.

When the electronic system 2230 is connected to a memory card to increase the storage capacity of the mobile system 2000, the functional unit 2230 serves as a memory card controller. In addition, when the mobile system 2000 further includes a universal serial bus (USB) to expand functions thereof, the functional unit 2230 may serve as an interface controller.

Each of the MP 2210, the power supply 2220, and the function unit 2230 includes a semiconductor device according to various exemplary embodiments of the inventive concept. Accordingly, operation speeds of the MP 2210, the power supply 2220, and the function unit 2230 may be increased.

FIG. 8 is a diagram of a mobile device 3000 including a semiconductor device according to an exemplary embodiment of the inventive concept.

Referring to FIG. 8, the mobile device 3000 may be a mobile wireless phone. Alternatively, the mobile device 3000 may be a tablet personal computer (PC). The mobile device 3000 may include a semiconductor device according to an exemplary embodiment of the inventive concept. Thus, operation speed of the mobile device 3000 according to an exemplary embodiment of the inventive concept may be increased.

FIG. 9 is a construction diagram of an electronic system 4000 including a semiconductor device according to an exemplary embodiment of the inventive concept.

Referring to FIG. 9, the electronic system 4000 includes a memory 4100, an MP 4200, a power supply 4300, and a user interface 4400. The electronic system 3000 may include a light-emitting diode (LED) illumination system, a refrigerator, an air conditioner, an industrial cutter, a welding machine, an automobile, a vessel, an airplane, or an artificial satellite.

The memory 4100 may store codes for booting the MP 4200, data processed by the MP 4200, or external input data. The memory 4100 may include a controller and a memory.

The MP 4200 may program and control the electronic system 4000. The MP 4200 may include a random access memory (RAM) used as an operation memory.

The power supply 4300 may receive a predetermined voltage from an external power supply and supply appropriate voltages to the memory 4100, the MP 4200, and the user interface 400 using the received voltage. The power supply 4300 may include a PMIC.

The user interface 4400 may communicate data using a bus 4500. The user interface 4400 may be used to input/output data to/from the electronic system 4000.

Each of the memory 4100 and the MP 4200 may include a semiconductor device according to an exemplary embodiment of the inventive concept. Accordingly, operation speeds of the memory 4100 and the MP 4200 may be increased.

According to an exemplary embodiment of the inventive concept, a semiconductor device may include a conductive pattern disposed within a trench formed through an interlayer insulating layer, side spacers disposed on side surfaces of the conductive pattern, and an air gap interposed between the trench and the side spacers. Thus, in a semiconductor device and a method of fabricating the same according to an exemplary embodiment of the inventive concept, a signal delay time of the conductive pattern may be reduced. Accordingly, in the semiconductor device and the method of fabricating the same according to an exemplary embodiment of the inventive concept, operation speed may be increased.

While the present inventive concept has been shown and described with reference to exemplary embodiments thereof, it will be apparent to those of ordinary skill in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the inventive concept as defined by the following claims. 

What is claimed is:
 1. A semiconductor device comprising: a semiconductor substrate; a lower conductive pattern disposed on the semiconductor substrate; an interlayer insulating layer disposed on the semiconductor substrate, the interlayer insulating layer including an upper penetrating hole partially exposing a top surface of the lower conductive pattern; an upper conductive pattern disposed within the upper penetrating hole and disposed on the top surface of the lower conductive pattern, the upper conductive pattern electrically connected to the lower conductive pattern; a side spacer disposed within the upper penetrating hole, the side spacer covering an upper side surface of the upper conductive pattern; and an air gap disposed within the upper penetrating hole, wherein a boundary of the air gap is bounded by a sidewall of the upper penetrating hole, the side spacer, part of the top surface of the lower conductive pattern, and a lower side surface of the upper conductive pattern, and wherein the side spacer is spaced apart from the lower conductive pattern by the air gap.
 2. The device of claim 1, wherein the lower side surface of the upper conductive pattern is not covered by the side spacer.
 3. The device of claim 1, wherein a highest level of the air gap is substantially the same as a level of a top surface of the upper conductive pattern.
 4. The device of claim 1, wherein each of the side spacer includes a first side surface being in contact with the upper side of the upper conductive pattern, and a second side surface facing the sidewall of the upper penetrating hole, wherein the second side surface of each of the side spacer is extended in parallel to the sidewall of the upper penetrating hole.
 5. The device of claim 1, wherein the top surface of the lower conductive pattern includes a first recess region, wherein the first recess region corresponds to the part of the lower conductive pattern bounding the air gap.
 6. The device of claim 5, wherein a lowest level of the air gap is substantially the same as a level of a bottom surface of the first recess region.
 7. The device of claim 5, wherein the top surface of the lower conductive pattern further includes a second recess region located at a center region of the top surface of the lower conductive pattern, wherein a level of a bottom surface of the second recess region is lower than a level of a bottom surface of the first recess region.
 8. The device of claim 7, wherein a bottom portion of the upper conductive pattern covers sidewalls and a bottom of the second recess region.
 9. The device of claim 7, wherein a level of a bottom surface of the upper conductive pattern is substantially the same as a level of the bottom surface of the second recess region.
 10. The device of claim 9, wherein a horizontal length of the bottom surface of the upper conductive pattern is substantially equal to a horizontal length of the bottom surface of the second recess region.
 11. A semiconductor device comprising: a semiconductor substrate; a lower conductive pattern disposed on the semiconductor substrate; an interlayer insulating layer disposed on the semiconductor substrate, the interlayer insulating layer including an upper penetrating hole partially exposing a top surface of the lower conductive pattern; an upper conductive pattern disposed within the upper penetrating hole and disposed on the top surface of the lower conductive pattern, the upper conductive pattern electrically connected to the lower conductive pattern; a side spacer disposed within the upper penetrating hole, the side spacer covering an upper side surface of the upper conductive pattern; and an air gap disposed within the upper penetrating hole, wherein the air gap is bounded by a sidewall of the upper penetrating hole, the side spacer, part of the top surface of the lower conductive pattern, and a lower side surface of the upper conductive pattern, wherein a horizontal length of the air gap between a sidewall of the upper penetrating hole and a side surface of the side spacer is substantially equal to a vertical length of the air gap between the top surface of the lower conductive pattern and a bottom surface of the side spacer.
 12. The device of claim 11, wherein the lower side surface of the upper conductive pattern is not covered by the side spacer.
 13. The device of claim 11, wherein a highest level of the air gap is substantially the same as a level of a top surface of the upper conductive pattern.
 14. The device of claim 11, wherein the horizontal length of the air gap is greater than a horizontal width of the side spacer.
 15. The device of claim 11, wherein the top surface of the lower conductive pattern includes a first recess region, wherein the first recess region corresponds to the part of the lower conductive pattern bounding the air gap.
 16. The device of claim 15, wherein a lowest level of the air gap is substantially the same as a level of a bottom surface of the first recess region.
 17. The device of claim 15, wherein the top surface of the lower conductive pattern further includes a second recess region located at a center region of the top surface of the lower conductive pattern, wherein a level of a bottom surface of the second recess region is lower than a level of a bottom surface of the first recess region.
 18. The device of claim 17, wherein a bottom portion of the upper conductive pattern covers sidewalls and a bottom of the second recess region.
 19. The device of claim 17, wherein a level of a bottom surface of the upper conductive pattern is substantially the same as a level of the bottom surface of the second recess region.
 20. The device of claim 19, wherein a horizontal length of the bottom surface of the upper conductive pattern is substantially equal to a horizontal length of the bottom surface of the second recess region. 